About 1.5 million years ago, a big-toothed cousin of prehistoric humans walked briskly along a lake in Kenyafootprints marking the muddy ground. But they weren’t our only ancestor on the scene: the early human Homo erectus trod the same ground..
Researchers say an analysis of fossilized footprints discovered in deposits of the Turkana Basin, northern Kenya, suggests the marks were made by two different species on the human family tree that were in the same place within hours or days of each other.
While skeletal fossils have previously suggested that these species may have coexisted, the length of time to which they can be dated, and the size of the deposits in which they are found, are too large to establish interactions.
“This is the first direct photograph of the two species together on the same immediate landscape,” says Dr Kevin Hatala, the first author of the research from Chatham University in the US.
Write in the journal ScienceHatala and colleagues reported how, along with fossilized tracks of birds and other animals, they discovered a continuous set of footprints in the deposits made by a single hominin individual.
The stride length of the track, they noted, suggests that the person was walking at a modestly fast pace. However, the impressions differed from those observed in modern humans in terms of foot anatomy and the contact patterns made by walking.
Instead, they said, the impressions appear to match the footprints expected from Paranthropus boisei, a species also known as Nutcracker Man in reference to his big teethwhich is not a human ancestor but sits on a side branch of our family tree.
“In particular, there are aspects of their big toe anatomy that match the patterns we see in the footprints,” Hatala said.
The team also found three separate prints nearby that were in different orientations from this track.
These, the researchers said, look similar to those observed in modern humans, suggesting they were made by Homo erectus, an ancestor of our own species who lived in the region at the time.
“I would expect that the two species would have been aware of each other’s existence on that landscape, and they probably would have recognized each other as ‘different,'” Hatala said. “It raises a lot of fascinating questions about how they would have interacted, and we don’t have all those answers yet.”
The researchers added that when they looked back at other examples of fossilized hominin footprints found in eastern Turkana from a similar period, they realized some also showed signs of being made by two different hominin species.
Prof Chris Stringer, the head of human origins at the Natural History Museum in London who was not involved in the work, described the research as fascinating and noted that although it was impossible to be absolutely sure which species made the tracks , the team was cautious in assessing the probabilities.
“It’s amazing that these early human relatives can now be placed directly in a lake landscape, walking and wading on wet surfaces, and probably feeding on the plant and animal resources there,” he said. “[The authors] suggests that the two species with their different diets probably did not compete strongly at this time, hence their close and tolerable proximity in time and space.”
